Wound treatment employing reduced pressure

ABSTRACT

A method of treating tissue damage comprises applying a negative pressure to a wound sufficient in time and magnitude to promote tissue migration and thus facilitate closure of the wound. The method is applicable to wounds, burns, infected wounds, and live tissue attachments. A wound treatment apparatus is provided in which a fluid impermeable wound cover is sealed over a wound site. A screen in the form of an open-cell foam screen or a rigid porous screen is placed beneath the wound cover over the wound. A vacuum pump supplies suction within the wound cover over the treatment site.

FIELD OF THE INVENTION

[0001] The present invention relates to an apparatus and method fortreating a wound by applying reduced pressure to the wound.

BACKGROUND OF THE INVENTION

[0002] The treatment of open wounds that are too large to spontaneouslyclose has long been a troublesome area of medical practice. Closure ofan open wound requires inward migration of surrounding epithelial andsubcutaneous tissue. Some wounds, however, are sufficiently large orinfected that they are unable to heal spontaneously. In such instances,a zone of stasis in which localized edema restricts the flow of blood tothe epithelial and subcutaneous tissue forms near the surface of thewound. Without sufficient blood flow, the wound is unable tosuccessfully fight bacterial infection and is accordingly unable toclose spontaneously.

[0003] An initial stage of wound healing is characterized by theformation of granulation tissue which is a matrix of collagen,fibronectin, and hyaluronic acid carrying macrophages, fibroblasts, andneovasculature that forms the basis for subsequent epithelialization ofthe wound. Infection and poor vascularization hinder the formation ofgranulation tissue within wounded tissue, thereby inhibiting woundhealing. It therefore becomes desirable to provide a technique forincreasing blood circulation within wounded tissue to promotespontaneous healing and to reduce infection.

[0004] Poor blood circulation and infection at the wound may also hinderattachment of skin grafts or flaps upon wounded tissue. Skin grafts andflaps will not attach to tissue that is poorly vascularized, infected ornecrotic. However, grafts and flaps can be used with much greatersuccess on tissue that, although wounded, is able to form granulationtissue. Accordingly, a technique for promoting blood circulation at thewounded tissue would also promote successful attachment, or “take,” ofskin grafts or flaps to the wounded tissue as a consequence of increasedblood circulation within the grafts or flaps.

[0005] Another problem encountered during the treatment of wounds is theselection of an appropriate technique for wound closure during thehealing process. Sutures are often used to apply force to adjacentviable tissue in order to induce the edges of a wound to migratetogether and heal. However, sutures apply a closure force to only a verysmall percentage of the area surrounding a wound. When there isscarring, edema, or insufficient tissue, the tension produced by thesutures can become great causing excessive pressure to be exerted by thesutures upon the tissue adjacent to each suture. As a result, theadjacent tissue often becomes ischemic thereby rendering suturing oflarge wounds counterproductive. If the quantity or size of the suturesis increased to reduce the tension required of any single suture, thequantity of foreign material within the wound is concomitantly increasedand the wound is more apt to become infected. Additionally, the size ortype of a particular wound may prevent the use of sutures to promotewound closure. It therefore becomes desirable to provide an apparatusand method for closing a large wound that distributes a closure forceevenly about the periphery of the wound.

[0006] Wounds resulting from ischemia, or lack of blood flow, are alsooften difficult to heal since decreased blood flow to a wound mayinhibit normal immune reaction to fight infection. Patients that arebedridden or otherwise non-ambulatory are susceptible to such ischemicwounds as decubitus ulcers or pressure sores. Decubitus ulcers form as aresult of constant compression of the skin surface and underlying tissuethus restricting circulation. Since the patient is often unable to feelthe wound or to move sufficiently to relieve the pressure, such woundscan become self-perpetuating. Although it is common to treat such woundswith flaps, the conditions that initially caused the wound may also workagainst successful flap attachment. Wheelchair-bound paraplegics, forexample, must still remain seated after treatment of pelvic pressuresores. It therefore becomes desirable to provide a treatment procedurefor ischemic wounds that can be conducted in situ upon an immobile orpartially mobile patient.

[0007] Other types of wounds in which ischemia leads to progressivedeterioration include partial thickness burns. A partial thickness burnis a burn in which the cell death due to thermal trauma does not extendbelow the deepest epidermal structures such as hair follicles, sweatglands, or sebaceous glands. The progression of partial thickness burnsto deeper burns is a major problem in burn therapy. The ability tocontrol or diminish the depth of burns greatly enhances the prognosisfor burn patients and decreases morbidity resulting from burns. Partialthickness burns are formed of a zone of coagulation, which encompassestissue killed by thermal injury, and a zone of stasis. The zone ofstasis is a layer of tissue immediately beneath the zone of coagulation.Cells within the zone of stasis are viable, but the blood flow is staticbecause of collapse of vascular structures due to localized edema.Unless blood flow is re-established within the zone of stasis soon afterinjury, the tissue within the zone of stasis also dies. The death oftissue within the zone of stasis is caused by lack of oxygen andnutrients, reperfusion injury (re-establishment of blood flow afterprolonged ischemia), and decreased migration of white blood is cells tothe zone resulting in bacterial proliferation. Again, it becomesdesirable to provide a technique for treating burn wounds by enhancingblood circulation to the wounded tissue to inhibit burn penetration.

SUMMARY OF THE INVENTION

[0008] In accordance with the present invention a wound treatmentapparatus is provided for treating a wound by applying reduced pressure(i.e. pressure that is below ambient atmospheric pressure) to the woundin a controlled manner for a selected time period. The application ofreduced pressure to a wound provides such benefits as faster healing,increased formation of granulation tissue, closure of chronic openwounds, reduction of bacterial density within wounds, inhibition of burnpenetration, and enhancement of flap and graft attachment. Wounds thathave exhibited positive response to treatment by the application ofnegative pressure include infected open wounds, decubitus ulcers,dehisced incisions, partial thickness burns, and various lesions towhich flaps or grafts have been attached.

[0009] The wound treatment apparatus in accordance with the presentinvention includes a reduced pressure application appliance which isapplied to a treatment site at which there is a wound and normal tissuesurrounding the wound. The reduced pressure application applianceincludes a fluid impermeable wound cover for covering and enclosing thewound. The appliance also includes sealing means for sealing the woundcover to the surrounding tissue of the wound in order to maintainreduced pressure in the vicinity of the wound during wound treatment.When the wound cover is sealed in position over the wound site, agenerally fluid-tight or gas-tight sealed enclosure is formed over thewound site. The sealing means may be in the form of an adhesive appliedto the underside of the wound cover for sealing the wound cover aroundthe periphery of the wound. The sealing means may also include aseparate sealing member such as an adhesive strip or a sealing ring inthe form of a tubular pad or inflatable cuff secured to the wound coverfor positioning around the periphery of the wound. In selectedembodiments, the reduced pressure within the sealed enclosure under thewound cover may serve to seal the wound cover in position at the woundsite. The reduced pressure appliance also includes a suction port forsupplying reduced pressure within the sealed volume enclosed beneath thewound cover. The suction port may be in the form of a nipple on thewound cover. Alternatively, the suction port may be in the form of atube attached to the wound cover or provided as a feedthrough beneaththe wound cover. The appliance may also include a porous wound screenfor placement in the wound or in position overlying the wound in orderto prevent overgrowth of wound tissue during treatment. The wound screenis sufficiently porous to permit gas flow to the wound. The porous woundscreen may be in the form of a sponge or open-cell foam material forplacement in the wound. The porous screen may also include a rigid orsemi-rigid screen for overlying the wound.

[0010] A vacuum system is connected with the reduced pressure appliancein order to provide suction or reduced pressure to the appliance. Forthis purpose, the vacuum system includes a suction pump or suctiondevice for connection with the suction port of the appliance forproducing the reduced pressure over the wound site. The vacuum systemmay include a section of hose or tube, such as a vacuum hose, thatinterconnects the suction device with the suction port of the applianceto provide the reduced pressure at the wound site. A collection devicein the form of a fluid trap may be provided intermediate the vacuum hoseof the suction device and the suction port of the appliance to trap anyexudate which may be aspirated from the wound by the-negative pressureappliance. A stop mechanism may also be provided for the vacuum systemto halt production of the reduced pressure at the wound site in theevent that an excessive quantity of exudate has been collected. Theapparatus may also include a control device for controlling the pump andfor providing intermittent or cyclic production of reduced pressure.

[0011] In a particular embodiment of the invention, the wound cover forthe reduced pressure appliance may be in the form of a gas impermeablecovering sheet of flexible polymer material, such as polyethylene,having an adhesive backing that provides the seal for securing the sheetover the wound site to provide an gas-tight or fluid-tight sealedenclosure over the wound site. The vacuum system of the wound treatmentapparatus may include a suction pump having a vacuum hose that isconnected with a suction tube serving as a suction port for theappliance. The suction tube for the appliance runs beneath the coversheet that is sealed in position over the wound site and into thefluid-tight enclosure provided under the cover sheet. An adhesivebacking on the cover sheet is used to provide a fluid-tight seal aroundthe feedthrough for the suction tube at the wound site. Within theenclosure, the suction tube is connected with a piece of open-cell foamfor placement in the wound. The open-cell foam functions to moreuniformly apply reduced pressure or suction over the wound site whileholding the cover sheet substantially out of the wound during theapplication of reduced pressure at the enclosed wound site.

[0012] In operation, a method of treating tissue damage is providedwhich comprises applying a negative or reduced pressure to a wound overan area sufficient to promote the migration of epithelial-andsubcutaneous tissue toward the wound and for a time period sufficient tofacilitate closure of the wound. The method is useful for treatingpressure sores.

[0013] A method of treating a burn wound is also provided whichcomprises applying a negative or reduced pressure to the burn over anarea and for a time sufficient to inhibit progression in the depth ofthe burn. The method is useful on a partial thickness burn soon afterits infliction.

[0014] A method of treating tissue damage is also provided whichcomprises applying a negative or reduced pressure to a wound for a timesufficient to reduce bacterial density in the wound. One use of thismethod is its application to a wound for a selected time period such asat least three days to reduce the bacterial density of an infected woundto the point at which surgical closure can be attempted.

[0015] Another aspect of the invention is a method of enhancing theattachment of adjacent tissue to a wound which comprises applyingnegative or reduced pressure to a joined complex of the adjacent livingtissue and the wound at a sufficient magnitude of reduced pressure andfor a sufficient time duration to promote the migration of epithelialand subcutaneous tissue toward the complex. This method enhancesattachment of adjacent tissue to tissues of the wound edges. Another useof this method is to enhance attachment of an open skin graft to thewound tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The foregoing summary, as well as the following detaileddescription of the preferred embodiments of the present invention, willbe better understood when read in conjunction with the appendeddrawings, in which:

[0017]FIG. 1 is a schematic elevational view of a wound treatmentapparatus in accordance with the present invention in which a reducedpressure appliance, shown in partial section, includes a flexible, fluidimpermeable wound cover sealed over the wound and a foam wound screenpositioned in the wound, and in which a vacuum system provides reducedpressure within the wound cover of the appliance;

[0018]FIG. 2 is a schematic sectional elevational view of a reducedpressure appliance in accordance with another embodiment of the presentinvention having a rigid, fluid impermeable wound cover sealed over awound and a rigid or semi-rigid screen overlying the wound;

[0019]FIG. 3 is a schematic sectional elevational view of a reducedpressure appliance in accordance with another embodiment of the presentinvention having a rigid, fluid impermeable wound cover sealed over awound;

[0020]FIG. 4 is a schematic sectional elevational view of a reducedpressure appliance in accordance with another embodiment of the presentinvention having a semi-rigid, fluid impermeable cover enclosing a woundand a rigid or semi-rigid screen overlying the wound, with an overlyingflexible fluid impermeable cover sheet sealing the enclosure over thewound;

[0021]FIG. 5 is a schematic elevational view of a reduced pressureappliance, shown in partial section, in accordance with anotherembodiment of the present invention having a flexible, fluid impermeablewound cover over an inner rigid porous support cup;

[0022]FIG. 6 is a schematic elevational view of a reduced pressureappliance, shown in partial section, having a rigid outer frame withsupport legs for supporting a flexible, fluid impermeable sealing coverover a wound;

[0023]FIG. 7 is a schematic elevational view in partial section of analternative fluid collection device having a float valve for use in thevacuum system of FIG. 1;

[0024]FIG. 8 is a schematic view of an alternative vacuum system;

[0025]FIG. 9 is a schematic view of an alternative vacuum systemincorporating a fluid collection device having an actuator forde-activating the vacuum system upon collection of a predeterminedquantity of fluid;

[0026]FIG. 10 is a schematic cross-sectional view of a reduced ornegative pressure appliance comprising an open-cell polymer foam screen,a flexible hose for connecting the foam screen with a vacuum system, andan adhesive-backed flexible polymer sheet overlying the foam-hoseassembly to provide a seal over a wound; and

[0027]FIG. 11 is a schematic cross-sectional view of a reduced ornegative pressure appliance comprising a rigid porous screen for awound, a rigid or semi-rigid cup for covering the wound having aninflatable cuff attached about the base of the cup, and a flexible hoseextending from the cup for connection with a vacuum system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] In accordance with the present invention, a wound treatmentapparatus is provided for treating a wound by application of reducedpressure (i.e., below atmospheric pressure) so that suction may beapplied to a wound site in a controlled manner for a selected timeperiod. As schematically shown in FIG. 10, a wound treatment apparatusincludes a reduced pressure appliance, generally designated 600, whichis applied to a wound site to treat the wound through the application ofreduced pressure. The appliance 600 is sealed in position over the woundsite to create a generally fluid-tight or gas-tight enclosure over thewound site.

[0029] The appliance 600 includes a substantially flat section of opencell polyester foam section 610 (Fischer Scientific, Pittsburgh, Pa.15219) sufficiently large to cover the wound and thus prevent woundovergrowth, a flexible hollow tube 611 (Fischer Scientific) insertedinto the open cell foam section 610 and joined thereto with an adhesiveand extending to attach at its opposite end with a Gast Vacuum pump(Fischer Scientific), and an Ioban adhesive sheet 612 (Minnesota Miningand Manufacturing, St. Paul, Minn. 55144) overlying the foam section 610and tubing 611 and adhered to the skin surrounding the wound, thusforming a seal that allows creation of a vacuum when the suction pumpoperates. Such an appliance 600 would most preferably be packaged in asterile condition to ameliorate the need for sterilization of theapparatus prior to use. The adhesive sheet 612 may be packagedseparately from the foam-tube assembly 610 and 611. A particularadvantage of this configuration is its use with pressure sores becausethe device can be placed in the depths of the wound and the patient canlie upon the device without either affecting the utility of the deviceor further damaging the wound. This becomes critical if the patientcannot be moved from this posture for medical or other reasons.

[0030] As shown in FIG. 11, a reduced pressure appliance, generallydesignated 615, in accordance with another embodiment of the presentinvention, is schematically depicted. The reduced pressure appliance 615includes an adult CPR mask 620 (Doug Brown and Associates, HuntingtonBeach, Calif. 92648) comprising a rigid or semi-rigid fluid impermeablecup 621 having an inflatable cuff 622 mounted around the periphery ofthe base of the cup 622 for contact with the skin, an open cellpolyester screen 624 overlying the wound, and a flexible ¼ inch diameterhose 623 (Fischer Scientific) connected by a Nalgene tubing connectorextending through a sealed hole in the cup for connection with a vacuumpump (Fischer Scientific). The hose 623 is connected with the pump 40 ofa vacuum system 30 of the type shown in FIG. 1 to provide reducedpressure within the cup 621. The vacuum created within the cup 621 bythe vacuum system may be sufficient to seal the cup in position over thewound site. Alternatively, fluid impermeable adhesive covering or stripsmay also be used to seal the appliance 615 in proper position.

[0031] Referring to FIG. 1, a wound treatment apparatus, generallydesignated 25, is depicted having a reduced pressure appliance 29 forenclosing a wound site to provide a fluid-tight or gas-tight enclosureover the wound site to effect treatment of a wound 24 with reduced ornegative pressure. The wound treatment apparatus 25 includes a reducedpressure appliance, generally designated 29, which is applied to andsealed over a wound site in order to enclose the wound site fortreatment with suction or reduced pressure within a sealed generallyfluid-tight or gas-tight enclosure. For the purpose of creating suctionwithin the appliance 29, the appliance 29 is connected with a vacuumsystem, generally designed 30, to provide a source of suction or reducedpressure for the sealed appliance 29 at the wound site. The appliance 29includes a fluid-impermeable wound cover 18 in the form of a flexible,adhesive, fluid impermeable polymer sheet for covering and enclosing thewound 24 and the surrounding normal skin 22 at the wound site. The woundcover 18 includes an adhesive backing 20 which functions to seal thewound cover to the normal skin 22 around the periphery of wound 24 toprovide a generally gas-tight or fluid-tight enclosure over the wound24. The adhesive cover sheet 18 must have sufficient adhesion to form afluid-tight or gas-tight seal 19 around the periphery of the wound andto hold the sheet 18 in sealed contact with the skin during theapplication of suction or reduced or negative pressure.

[0032] The appliance 29 also includes a porous wound screen 10 which isplaced within the wound 24. The wound screen 10 is placed oversubstantially the expanse of the wound to prevent its overgrowth. Thesize and configuration of the wound screen 10 can be adjusted to fit theindividual wound. It can be formed from a variety of porous materials.The material should be sufficiently porous to allow oxygen to reach thewound. The wound screen 610 may be in the form of an open-cell polymerfoam, such as a polyurethane foam, which is sufficiently porous to allowgas flow to and/or from the wound 24. Foams may be used that vary inthickness and rigidity, although it may be desirable to use a spongymaterial for the patient's comfort if the patient must lie upon theappliance during treatment. The foam may also be perforated to enhancegas flow and to reduce the weight of the appliance. As shown in FIG. 1,the screen 10 is cut to an appropriate shape and size to fit within thewound 24. Alternatively, the screen may be sufficiently large to overlapthe surrounding skin 22.

[0033] The appliance 29 also includes a suction port in the form of ahollow suction tube 12 that connects with the vacuum system 30 toprovide suction within the sealed enclosure. The suction tubing 12serves as a suction port for appliance 29. An end segment 12 a of thetubing 12 is embedded within the foam screen 10 for providing suction orreduced pressure within the enclosure provided under the wound cover 18.Embedding the open end of segment 12 a of tubing 12 within the interiorof the foam screen 10 permits the foam screen 10 to function as a shieldto help prevent the wound cover 18 from being inadvertently sucked intosealing engagement with the open end of the tube thereby plugging thetube 12 and restricting gas flow. The tube segment 12 a embedded withinthe foam screen 10 preferably has at least one side port 14 forpositioning within the interior of the foam screen 10 to promotesubstantially uniform application of reduced pressure throughout theenclosure. Positioning the side port 14 of tube segment 12 a within theinterior of the foam screen 10 permits the foam screen 10 to function asa shield for the side port to thereby prevent the wound cover 18 frombeing sucked into the side port 14 and thereby restricting gas flow. Theopen cells of the foam screen 10 facilitate gas flow throughout theenclosure. In addition, the foam screen 10 functions to prevent woundovergrowth and to hold the wound cover 18 generally out of contact withthe wound 24 during the application of suction within the enclosure.

[0034] Tubing 12 and tube segment 12 a are sufficiently flexible topermit movement of the tubing but are sufficiently rigid to resistconstriction when reduced pressure is supplied to the appliance 29 orwhen the location of the wound is such that the patient must sit or lieupon the tubing 12 or upon the reduced pressure appliance 29. Thescreen-tube assembly comprising the foam screen 10 and the tube 12 maybe fabricated by snaking the end of the tube segment 12 a through aninternal passageway in the foam screen 10 such as by pulling the end ofthe tube segment 12 a through the passageway using forceps.Alternatively, fabrication of the screen-tube assembly may beaccomplished by suspending the end of the tube segment 12 a into asuitable mold or form and then blowing foam into the mold or form toembed the tube end segment 12 a within the blow-molded foam screen. Thescreen-tube assembly 12 and 10 is preferably prepared prior to use understerile conditions and then stored in an aseptic package.

[0035] In order to use the reduced pressure appliance 29 at the site ofthe wound 24, the flexible, gas-impermeable, adhesive wound cover sheet18 is secured in position at the wound site overlying the foam screen 10disposed within the wound 24. The wound cover sheet 18 is secured andsealed to the surrounding normal skin 22 by an adhesive layer 20 on theunder surface of the wound cover 18 to form a gas-tight seal 19 aroundthe periphery of the wound 24. The wound cover 18 also provides agas-tight seal around the tubing 12 at the feedthrough location 22 awhere the tubing 12 emerges from beneath the wound cover 18. The woundcover 18 is preferably formed of a fluid impermeable or gas impermeableflexible adhesive sheet such as Ioban, a product of the 3M corporationof Minneapolis, Minn.

[0036] The vacuum system 30 includes a suction pump 40 that produces asource of reduced pressure or suction which is supplied to the reducedpressure appliance 29 by suction tubing 12. As shown in FIG. 1, a fluidtrap, generally designated 28, is interconnected between the suctionpump 40 and the appliance 29 to remove and collect any exudate which maybe aspirated from the wound 24 by the reduced pressure appliance. Theappliance 29 functions to actively draw fluid or exudate from the wound24. Collection of exudate in a fluid trap 28 intermediate the pump 40and the appliance 29 is desirable to prevent clogging of the pump 40. Asuitable fluid trap 28 may be assembled from an Erlenmeyer or side-armflask 31 having a top opening and a side-arm opening. The fluid trap 28includes a first port 32 at the top opening of the flask for sealedconnection to suction tubing 12. The first port 32 enables suction to beapplied to the reduced pressure appliance 29 through the tubing 12 andalso enables exudate from the wound covered by reduced pressureappliance 29 to be drained into the flask 31. The flask 31 provides acollecting vessel 33 for the fluid trap for containing and temporarilystoring the collected exudate. A suction port 34 is provided at theside-arm opening of the flask to enable the application of suction fromvacuum pump 40. The suction port 34 of the fluid trap 28 is connected tothe vacuum pump 40 by vacuum line 36. The fluid trap 28 is sealedgenerally gas-tight to enable the suction pump 40 to supply suction tothe appliance 29 through the fluid trap 28. A filter 38 such asmicropore filter is preferably attached to the exhaust of the pump 40 toprevent potentially pathogenic microbes or aerosols from being vented toatmosphere by the vacuum pump 40.

[0037] Predetermined amounts of suction or reduced pressure are producedby the vacuum pump 40. The vacuum pump 40 is preferably controlled by acontrol device 44 such as a switch or a timer which may be set toprovide cyclic on/off operation of the vacuum pump 40 according touser-selected intervals. Alternatively, the vacuum pump 40 may beoperated continuously without the use of a cyclical timer.

[0038] The vacuum system 30 preferably includes a shut-off mechanism forhalting or inhibiting the supply of the reduced pressure to theappliance 29 in the event that the exudate aspirated from the wound 24exceeds a predetermined quantity. Interrupting the application ofsuction to the appliance 29 is desirable to prevent exsanguination inthe unlikely event a blood vessel ruptures under the wound cover 18during treatment. If, for example, a blood vessel ruptures in thevicinity of the wound 24, a shut-off mechanism would be useful toprevent the vacuum system 30 from aspirating any significant quantity ofblood from the patient. As a safety feature, various mechanical orelectrical detection mechanisms may be employed to detect the level ofexudate in the fluid trap 28.

[0039] As shown in FIG. 7, a fluid trap 28 employing a collection bottleor flask 35 is provided for connection intermediate the pump 40 and theappliance 29 for collecting exudate from the wound site. The flask 35has a side-arm port 43 connected to suction tube 12 leading to thereduced pressure appliance 29 and a suction port 34 located at the top44 of the flask 35 connected to the vacuum hose 36 leading to the vacuumpump 40. For the purpose of detecting liquid level within the flask 35,a float valve assembly, generally designated 39, is provided. Thefloat-valve assembly 39 functions to close and seal off the suction port34 of the fluid trap 28 when the quantity of exudate in the collectingvessel 33 exceeds a predetermined quantity. The float valve assembly 39is provided in the form of a ball 46 which is held and suspended withina cage 47 positioned below a valve seat 48 disposed within the openingat the top 44 of the flask 35. The ball 46 has a specific gravity belowthat of the exudate so that the ball 46 will float upon the exudate andwill be lifted against the valve seat 48 as the vessel 33 fills withexudate. When the ball 46 is firmly seated against the valve seat 48,the float valve 39 blocks suction port 34 and thereby shuts off thesource of suction from vacuum line 36. The suction within the appliance29 at the wound site arrests thus halting the aspiration of exudate fromthe wound.

[0040] Other types of mechanisms may be employed to detect the liquidlevel within the fluid trap 28 in order to arrest operation of thevacuum source. An alternative vacuum system 30 a is shown in FIG. 8 inwhich a filter 38 a is employed in vacuum line 36 for filtering thefluid or gas flow through the vacuum line 36 and for detecting the levelof liquid in fluid trap 28. Exudate from the wound is collected invessel 33. When the vessel 33 becomes full, aspiration of furtherexudate from the wound causes the vacuum line 36 to begin to collectexudate which eventually reaches the in-line filter 38 a positioned inthe vacuum line 36 intermediate the fluid trap 28 and the pump 40 ahaving operational control 44 a. The filter 38 a contains a filterelement that is selected to clog when exposed to sufficient amounts ofmoisture to thereby halt the supply of suction through the fluid trap 28to the appliance 29. The filter 38 a is preferably an in-line,disc-shaped submicron filter having a nitrocellulose or PTFE filtrationelement for filtering particles larger than about 0.1 μm from the vacuumline 36. In addition to preventing excess fluid aspiration, the filter38 a in the vacuum line 36 prevents contamination of the vacuum pump 40by filtering potentially pathogenic microbes and aerosols.

[0041] Other types of detection devices may also be employed to detect apredetermined level of liquid collected in collection vessel 33. Forexample, collection of exudate in excess of a predetermined quantity mayenable actuation of an electronic switch which turns off the vacuum pumpor otherwise halts the supply of suction to the reduced pressureappliance 29. Referring to FIG. 9, the suction tubing 12 from thereduced pressure appliance 29 is connected to a three-port couplingdevice 160 that interconnects suction tube 12, vacuum line 36 b andfluid collecting apparatus 131. The coupling device 160 permitstransmission of suction from the vacuum line 36 b of the pump 40 b tothe suction tubing 12. The coupling device 160 also permits aspiratedexudate from tubing 12 to be collected in an expandable container, suchas an intravenous fluid bag 162, housed beneath the coupling device 160in a rigid housing vessel 33 b. As exudate is collected, the bag 162expands to conform to the shape of the interior surface of thesurrounding rigid vessel 33 b. An actuator 166, such as a spring-loadedactuator switch, is located within the side wall of the rigid vessel 33b and functions to shut off the pump 40 b upon actuation of the switch166. When the bag 162 expands sufficiently to contact and actuate switch166 as shown in dashed lines at 162 a in FIG. 9, the switch 166 isopened and the supply of power to the pump 40 b along power line 164 isinterrupted and the supply of suction to the appliance 29 is stopped.The actuator switch 166 may also cooperate with control 44 b for thepump 40 b to stop operation of the pump 40 b. Other types of devices mayalso be employed to detect fluid levels in fluid trap 28. For example,weight detectors may be employed to detect a predetermined weight limitas the fluid trap fills with exudate or other liquid. Alternatively,optical sensors or detectors may also be employed.

[0042] For the purpose of protecting the site of a wound from impact orabrasion during treatment, a reduced pressure appliance employing arigid or semi-rigid wound cover may be utilized over the site of thewound. As shown in FIG. 2, a reduced pressure appliance 29 a includes aCPR mask 58 that provides a rigid wound cover for enclosing anappropriately-sized wound 74. The mask 59 is impermeable to fluids orgases so that a fluid-tight or gas-tight enclosure is effected over thewound site. The mask 59 is sufficiently rigid to support itself awayfrom the wound during the application of suction or reduced pressure sothat the mask 59 does not collapse into the wound 74. The CPR mask 58 isof the type having an inflatable air cuff 59 around the base of themask. The cuff 59 may be inflated via an external valve for sealing themask 59 against the normal skin 72 around the periphery of the wound 74.The air cuff 59 also prevents the base of the mask from digging into theskin 72 during application of reduced pressure. An optional screen 50for preventing overgrowth of the wound 74 may be positioned to overliethe wound 74. The screen 50 may be formed of a rigid or semi-rigidperforated polymer surgical mesh such as Prolene mesh. Alternatively, asection of honeycombed polyethylene sheet may be cut to a suitable sizeand shape to overlie the wound 74. The screen 50 is held against thesurrounding normal skin 72 in position overlying wound 74 by the cuff 59which overlaps at least a portion of the periphery of the screen 50. TheCPR mask 58 also includes a suction port in the form of a hose connector54 to which one end of a suction tube 52 is attached. The other end oftube 52 is connected with a vacuum system 30 of the type previouslydescribed to provide a source of suction or reduced pressure for theappliance 29 a. Suction produced within the appliance 29 a may besufficient to seal the cuff 59 to the skin and to thereby seal theappliance 29 a in position over the wound site. However, in order toensure a gas-tight seal between the reduced pressure appliance 29 a andthe surrounding skin 72, the mask 58 may also be secured to thetreatment site with a fluid impermeable adhesive seal 68. The adhesiveseal 68 may be formed of a flexible adhesive material such as anadhesive tape or an adhesive sheet that has been cut to surround and atleast partially overlie the cuff 59. As shown in FIG. 2, the adhesiveseal is secured to the base portion of the rigid mask 58 and to thenormal skin 72 around the periphery of the air cuff 59 to seal the maskin position over the wound site.

[0043] As shown in FIG. 3, a reduced pressure appliance 29 b is depictedhaving a rigid, fluid impermeable, cup-shaped wound cover 88 overlying awound site. The appliance 29 b is used to treat a wound 114 without anyscreen either in the wound or overlying the wound. The cover cup 88 canbe formed of a polymer such as polystyrene, HDPE, or other suitablyrigid material. The cup 88 must be sufficiently rigid to support itselfout of contact with the wound 114 during the application of suction ornegative pressure so that the cup 88 does not collapse into the wound.Reduced pressure is supplied to the interior of the cup 88 through thesuction tubing 82 connected to suction port 84 in the form of a nipplesealed in position on the cup 88. The tubing 82 is also connected with asuitable vacuum system 30 of the type previously described to provide asource of suction or negative pressure within the appliance 29 b. Thebase of the cup 88 supports an inflatable air cuff 89 to seal the cup 88to the skin and to prevent the cup 88 from digging into the skin 92 andcausing discomfort when reduced pressure is applied. The cuff 89 ispositioned upon the normal skin 92 surrounding the wound 94. While thesuction created within the cup 88 may be sufficient to hold theappliance in position by causing the air cuff to seal to the skin, moreeffective attachment of the appliance to the surrounding skin 92 may beobtained by the use of a strip of fluid impermeable, adhesive materialsecured to the skin 102 and to the base of the cup 88 over the air cuff89 around the periphery of the base of the cup 88. The layer of adhesivematerial 98 helps to ensure that a fluid-tight or gas-tight seal ismaintained between the cup 88 and the surrounding skin 92 so that afluid-tight enclosure is formed over the wound site.

[0044] Referring to FIG. 4, a reduced pressure appliance 29 c isdepicted for enclosing a wound site for the treatment of wound 114 withsuction or reduced pressure. The reduced pressure appliance 29 cincludes a fluid-impermeable wound covering, generally designated 116,having an outer flexible, adhesive polymer sheet 117 applied over aninner, generally circular, semi-rigid shield 118, such as a polystyreneshield, for covering and enclosing the wound site. The base of theshield 118 is positioned over a circular pad 109 which may be formedfrom flexible tubing to prevent the base of the cup from digging intothe skin 102 and causing discomfort when suction is applied to theappliance 29 c. The pad 109 may also facilitate sealing of the covershield 118 in position over the wound site to form a fluid-tight orgas-tight enclosure over the wound site. The pad 109 may be positioneddirectly onto the normal skin 102 surrounding the wound 114 or, as shownin FIG. 4, the pad 109 may overlie an outer peripheral portion of arigid screen 100 in order to hold the screen 100 in a position overlyingthe wound to prevent wound overgrowth. A suction port 104 is provided atthe top of the shield 118 to permit gas-tight connection to suction tube112. The suction port 104 may be in the form of a removable connectorthat is screwed into position at the top of the shield 118. Suction tube112 functions to connect the appliance 29 c to a suitable vacuum system30 of the type previously described. For the purpose of enhancing thesealing of the appliance 29 c in position over the wound site, anover-sized, generally circular, adhesive, fluid impermeable polymersheet 117 is adhered and secured to the top surface of the shield 118.The oversized adhesive sheet 117 extends beyond the outer periphery ofthe shield 118 so that the adhesive sheet 117 provides a sealing ring119 of material around the periphery of the shield. The sealing ring 119is sealed and adhered to the normal skin 102 around the outer peripheryof pad 109. When sealed in position overlying wound 114, the appliance29 c provides a generally fluid-tight or gas-tight enclosure over thewound site.

[0045] Referring to FIG. 5, a reduced pressure appliance 29 d isdepicted for enclosing and treating a wound 124 with suction or reducedpressure. A rigid or semirigid porous cup 138 is placed rim side downupon a porous screen or pad 120 located within a wound 124. The cup 138has perforations 133 for equalizing pressure inside and outside of thecup 138. A flexible, fluid impermeable adhesive polymer cover sheet 128is draped over the cup 138 to enclose the wound 124. The adhesive coversheet 128 is adhered and sealed to the top portion of the cup 138 and tothe surrounding normal skin 122 by adhesive layer 129 on the undersideof the cover sheet 128 to provide a fluid-tight enclosure beneath thesheet 128. The cup 138 provides a generally central support beneath thecover sheet 128 to hold the cover sheet 128 out of contact with thewound 124 during application of suction. The cup 138 has a centralsuction port 134 sealed in position at the top of the cup 128 to permitconnection by suction tube 132 to a vacuum system 30 of the typepreviously described. When reduced pressure is supplied to the appliance29 d, the cover sheet 128 is deformed downward and inward to position128 a as shown in phantom in FIG. 5. Tension developed within thedeformed sheet 128 a by virtue of the suction is exerted upon thesurrounding skin by the sheet at position 128 a. The outer periphery 124a of the wound 124 is pulled inward by virtue of such tension to theposition shown in phantom at 124 b to promote closure of the wound. Thetension within the sheet at position 128 a also exerts a downward forceupon the cup 138 which more firmly presses the cup 138 onto the wound124. Such downward force on the cup 138 may be desired in suchapplications as flap or graft attachment to promote contact between theflap or graft and the underlying tissue. The pad 124 under the cup 138helps to alleviate discomfort caused by the downward force on the cup138.

[0046] For applications where a downward pressure of the appliance intoa wound is not desired, a reduced pressure appliance 29 e, as shown inFIG. 6, may be utilized having a support structure, generally designated151, which is positioned external to a flexible sealing sheet 148 forcovering a wound 144. The flexible cover sheet 148 is in the form of aflexible, fluid impermeable, adhesive polymer sheet. The reducedpressure appliance 29 e shown in FIG. 6 includes an external supportframe 151 in the form of a series of spider-like legs 158 radiatingoutwardly from a central support hub 155. The legs 158 hold the centralhub 159 directly over the wound 144. A connector 153 is removablymounted to the hub 155 to permit a suction tube 152 to be connected withthe flexible cover sheet 148. The connector 153 may screw together andapart to permit the connector to be removably mounted relative to thehub 155. The flexible adhesive sheet 148 is adhered to the connector 153at hub 155 and to the surrounding normal skin 142 so that the sheet issuspended over the wound 144 from the hub 155 in tentlike fashion. Theflexible sheet is adhesively sealed to the connector 153 at the hub 155and is also adhesively sealed to the skin 142 around the periphery ofthe wound 144 to form a fluid-tight or gas-tight enclosure over thewound site. The legs 158 of the frame 153 extend radially outward fromthe hub 153 and stand upon feet members 159 which may rest upon theouter periphery of the sheet 148 to help hold the cover sheet 148 in aposition from being sucked together during the application of suction.Alternatively, the feet members 159 may extend beyond the cover sheet148 and may rest upon the surrounding tissue beyond the periphery of thecover sheet 148. The connector 153 supported on the hub 155 provides asuction port 154 through which suction is supplied to the appliance 29 evia suction tube 152. Tube 152 is connected to a vacuum system 30 of thetype previously described for supplying reduced pressure within thecover sheet 148. When suction or reduced pressure is introduced via port154, the sheet 148 deforms inwardly and downwardly to the position shownin phantom at 148 a thus developing tension which is exerted upon thesurrounding skin 142. The deformed sheet in position at 148 a pulls theedges of the wound 144 inwardly to the position indicated in phantom at144 b hence promoting closure of the wound 144.

[0047] Negative pressure appliances are useful for treating a variety ofwounds. Treatment of a wound can be carried out by securing a negativepressure appliance to the treatment site as previously shown anddescribed, and then maintaining a substantially continuous or cyclicalreduced pressure within the appliance until the wound has reached adesired improved condition. A selected state of improved condition mayinclude formation of granulation tissue sufficient for the attachment ofa flap or graft, reduction of microbial infection in the wound, arrestor reversal of burn penetration, closure of the wound, integration of aflap or graft with the underlying wounded tissue, complete healing ofthe wound, or other stages of improvement or healing appropriate to agiven type of wound or wound complex. It may be preferable to change theappliance periodically, such as at 48 hour intervals, during treatment,particularly when using appliances incorporating a screen on or in thewound. The method is preferably practiced using a negative or reducedpressure ranging from 0.01 to 0.99 atmospheres, and more preferablypracticed using a negative or reduced pressure ranging between 0.5 to0.8 atmospheres. The time period for use of the method on a wound maypreferably be at least 12 hours, but can be, for example, extended forone or more days. There is no upper limit beyond which use of the methodis no longer beneficial; the method increases the rate of closure up tothe time the wound actually closes. Satisfactory treatment of varioustypes of wounds has been obtained via the use of reduced pressuresequivalent to about 2 to 7 in. Hg below atmospheric pressure.

[0048] Supplying reduced pressure to the appliance in an intermittent orcyclic manner has also been demonstrated to be useful for treatingwounds. Intermittent or cyclic supply of reduced pressure to anappliance may be achieved by manual or automatic control of the vacuumsystem. A cycle ratio, the ratio of “on” time to “off” time, in such anintermittent reduced pressure treatment may be as low as 1:10 or as highas 10:1. The preferred ratio is approximately 1:1 which is usuallyaccomplished in alternating 5 minute intervals of reduced pressuresupply and non-supply.

[0049] A suitable vacuum system includes any suction pump capable ofproviding at least 0.1 pounds of suction to the wound, and preferably upto three pounds suction, and most preferably up to fourteen (14) poundssuction. The pump can be any ordinary suction pump suitable for medicalpurposes that is capable of providing the necessary suction. Thedimension of the tubing interconnecting the pump and the reducedpressure appliance is controlled by the pump's ability to provide thesuction level needed for operation. A ¼ inch diameter tube may besuitable.

[0050] The present invention also includes a method of treating damagedtissue which comprises the steps of applying negative pressure to awound for a selected time and at a selected magnitude sufficient toreduce bacterial density in the wound. Open wounds are almost alwayscontaminated with harmful bacteria. Generally a bacterial density of 10⁵bacterial organisms per gram of tissue is regarded as infected. It isgenerally accepted that at this level of infection, grafted tissue willnot adhere to a wound. These bacteria must be killed, either through thewound host's natural immune response or through some external method,before a wound will close. The application of negative pressure to awound appears to reduce the bacterial density of the wound. It isbelieved that this effect is due to either the bacteria'sincompatibility with a negative pressure environment or the increasedblood flow to the wound area, as blood brings with it cells and enzymesto destroy the bacteria. The method can be used to reduce bacterialdensity in a wound by at least half. More preferably, it can be used toreduce bacterial density by at least 1,000 fold. Most preferably, themethod can be used to reduce bacterial density by at least 1,000,000fold.

[0051] The present invention also includes a method of treating a burnwhich comprises the steps of applying negative pressure to the burn overan area with predetermined reduced pressure and for a time sufficient toinhibit formation of a full thickness burn. A partial thickness burn,one which has a surface layer of dead tissue and an underlying zone ofstasis, is often sufficiently infected so that it will transform within24-48 hours into a full thickness burn, one in which all epidermalstructures are destroyed. The application of negative pressure to thewound prevents the infection from becoming sufficiently severe to causedestruction of the underlying epidermal structures. The magnitude,pattern, and duration of pressure application can vary with theindividual wound.

[0052] The present invention also provides a method for enhancing theattachment of living tissue to a wound which comprises the steps offirst joining the living tissue to the wound to form a wound-tissuecomplex, then applying a negative or reduced pressure of selectedmagnitude to the wound-tissue complex over an area sufficient to promotemigration of epithelia and subcutaneous tissue toward the complex, withthe negative pressure being maintained for a selected time periodsufficient to facilitate closure of the wound. Attachment of livingtissue to a wound is a common procedure that can take many forms. Forexample, one common technique is the use of a “flap,” a technique inwhich skin tissue from an area adjacent to the wound is detached onthree sides but remains attached on the fourth, then is moved onto thewound. Another frequently used technique is an open skin graft in whichskin is fully detached from another skin surface and grafted onto thewound. The application of negative pressure to the wound-graft complexreduces bacterial density in the complex and improves blood flow to thewound, thereby improving the attachment of the grafted tissue. Furtherfeatures of the apparatus and methods for the use thereof shall be madeapparent in the following examples.

EXAMPLE 1

[0053] Treatment of Open Wounds

[0054] In order to demonstrate the use of a negative pressure appliancein the treatment of open wounds, an animal study was conducted usingpigs as subjects. Pigs are frequently used as subjects in wound healingstudies since they have essentially the same skin and subcutaneoustissue structure as humans.

[0055] Five 15 kg Chester pigs were obtained and acclimated for 1 weekprior to use. The animals were sedated with an intramuscular injectionof ketamine (25 mg/kg): xylazine (2.5 mg/kg): acepromazine (5 mg/kg).The backs and sides of the animals were shaved and scrubbed for surgery.One percent halothane was administered by endotracheal tube formaintenance of anesthesia. Two circular wounds were created on themidline of the animals. The wounds were 2.5 cm in diameter having adepth reaching, but not including, the deep fascia over the spine(approximately 1 cm). Wounds in pigs in this site do not contract duringhealing. Alginate impressions were made of each wound to determine thevolumes of the wounds.

[0056] A reduced pressure appliance of the type discussed in connectionwith FIGS. 2 and 11 was positioned over each wound, and the cups weresealed to the skin with an Ioban sheet. A non-compressible silicone tubewas attached to the anterior appliance of each pig and a reducedpressure of 5 in. Hg below atmospheric pressure was supplied to theanterior appliances. No reduced pressure was applied to the posteriorwounds. The animals were allowed to recover from anesthesia and givenfood and water ad libitum. The tubes were suspended from a pulley systemover the top of each pen arranged to provide each animal with full,unrestricted access to its pen.

[0057] The animals were sedated 48 hours after surgery as describedabove, and then daily thereafter, so that alginate impressions could bemade of each wound. This routine was continued until the wounded areaswere filled with granulation tissue until coplanar with the surroundingtissue. The results of this experiment, including time to completefilling of the wound space by granulation tissue and the rate ofgranulation tissue formation, are presented in Table 1. The data in thethird column of Table 1 shows the number of days needed for the treatedand non-treated wounds to heal. In order to allow comparisons betweenthe healing rate of variously-sized wounds, the data in the fourthcolumn is expressed as a healing rate in terms of cc granulation tissueper day. As can be seen, the treated wounds exhibited higher rates ofhealing than did the non-treated wounds. The wounds treated with reducedpressure filled with granulation tissue at an average rate that was52.3% greater than the rate of granulation of the control wounds.

[0058] Animals numbered 1 and 2 experienced intermittent loss of reducedpressure throughout the experiment, yet the treated wounds of theseanimals also healed significantly faster than their control wounds.TABLE 1 Initial % Rate Wound Increase Volume Days to Full Fill Rate Dueto Animal Wound (cm³) Granulation (cm³/day) Treatment #1 Control 4.9 130.38 Treated 5.3 11 0.48 26.3 #2 Control 7.2 8 0.90 Treated 9.3 8 1.1628.9 #3 Control 4.0 12 0.33 Treated 3.5 6 0.58 75.8 #4 Control 4.7 110.43 Treated 5.0 7 0.71 65.1 #5 Control 4.7 11 0.43 Treated 5.1 7 0.7165.1 Average — — — — 52.3

EXAMPLE 2

[0059] Reduction of Infection

[0060] During the course of the experiment described as Example 1 above,it was observed that the reduced pressure-treated wounds were muchcleaner and bled more spontaneously than non-treated wounds. It wastherefore undertaken to determine the relative rates of clearance of aknown bacterial inoculum from treated and non-treated wounds.

[0061] Five 15 kg pigs were obtained and wounds created as set forth inExample 1. Two 2.5 cm diameter defects were created on the dorsum ofeach pig using a sterile technique, with a 7.5 cm interval retainedbetween the edges of the defects. Hemostasis was obtained byelectrocautery. Prior to placement of the reduced pressure appliances,10⁸ organisms of Staphylococcus aureus in 1 ml saline solution wereinjected into each wound. The reduced pressure appliances of the typeshown in FIGS. 2 and 11 were then attached as in Example 1. A reducedpressure of 5 in. Hg below atmospheric pressure was applied to one ofthe wounds upon each animal. Reduced pressure was not applied to theother wound upon each animal. T-shirts were placed over the animals andno antibiotics were given during the course of the study. The animalswere sedated as in Example 1 at 24 hour intervals, and a 3 mm diameterfull thickness biopsy was taken from each wound site daily. The deviceswere then reattached and reduced pressure re-applied. This routine wascontinued for one week.

[0062] The biopsy samples were weighed and sterile saline (99× biopsyweight) added. The tissue samples were homogenized in a tissue grinderand serial dilutions were made in triplicate. 100 microliters of eachdilution was plated on a blood agar plate and incubated overnight. Thenumber of colonies were counted on each plate and thus the number oforganisms per gram of tissue was calculated. The data was recorded asthe common logarithm of the number of organisms/gram tissue and is shownin Table 2. TABLE 2 Average Log₁₀ (organisms/gm) Day Day 0 Day 1 Day 2Day 3 Day 4 Day 5 7 Control 8.44 8.04 8.17 7.13 7.13 8.82 7.08 Treated7.69 7.36 7.37 6.79 6.43 3.98 4.32

[0063] As can be seen in Table 2, the common logarithm of the averagenumber of organisms per gram of tissue present in the treated andnon-treated wounds decreased slightly for all five animals over thefirst 4 days. In the treated wounds, the mean log of organisms/gmdecreased dramatically between days 4 and 5. The mean log oforganisms/gm within the non-treated wounds increased during the sameperiod. Using the traditional baseline of 10⁵ organisms/gm to defineinfection, the data of Table 2 shows that the average treated wound wasdisinfected after four days of treatment while the average non-treatedwound was still infected after 7 days.

EXAMPLE 3

[0064] Treatment of Burns

[0065] Use of reduced pressure appliances upon burns has been found toretard the progression of partial thickness burns into full thicknessburns. A partial thickness burn is a burn in which the depth of celldeath due to thermal trauma does not extend below the level of thedeepest epidermal structures (i.e., the base of hair follicles, sweatglands, sebaceous glands, etc.). A burn that is initially a partialthickness burn will often deepen and progress into a full thickness burndue to insufficient blood circulation to the epidermal cells beneath thepartial burn.

EXAMPLE 3A

[0066] The backs of five 15 kg pigs were shaved and scrubbed forsurgery. A 1.5 inch diameter brass rod was heated to 190° C. in an oilbath. The rod was pressed onto the pig's skin for 15 seconds following awell-known technique of relating depth of burn to time and temperature.Three burns were created over the spine of each pig, separated by 5 cmintervals. Suction apparatus cups of the configuration shown in FIGS. 2and 11 were placed over two of the burns, with silver sulphadiazine(silvadine) cream, the standard antibiotic cream applied to human burnsprior to excision of burned tissue, applied to the third. Cefaxolin(Kefzol) (500 mg) was administered intramuscularly (antibiotic). Suction(2-6 pounds vacuum) was applied to one of the cups. A small (2 mm) punchbiopsy was taken of the wounded area and examined histologically fordepth of burn.

[0067] Biopsies were analyzed by a dermatopathologist who was not toldthe nature of the study. It was concluded that the suctioned tissuespecimens were healthier and healing more quickly than non-suctionedspecimens.

EXAMPLE 3B

[0068] A set of 2 cm diameter standardized depth partial thickness burnswere created by pressing a heated metal rod to each side of fiveanesthetized pigs to create 16 burns on each side of each pig. Reducedpressure appliances of the type shown in FIGS. 2 and 11 were securedover each of the burns on the left side of each animal and a continuouspressure of 6 in. Hg was supplied to the reduced pressure appliances.The animals were anesthetized daily, and elliptical full-thicknessbiopsies extending from non-injured tissue, through the center of eachburn, and into non-injured tissue were harvested, fixed in formalin,processed for histological analysis and stained with Hematoxylin/eosinand Gomori's trichrome. The histologic slides were then given to aDermatopathologist for blind determination of burn depth according tothe Breslow Local Scale of maximum depth of cell death below the surfaceof the skin.

[0069] The Breslow Level (maximum total depth) for the burns treated byreduced pressure was 0.095 mm. The maximum depth of the burns which werenot treated by reduced pressure was 0.885 mm. The use of reducedpressure appliances thus resulted in a 112% reduction in the maximumdepth of burn progression.

EXAMPLE 3C

[0070] Treatment of Burn With Negative Pressure

[0071] Patient B. is admitted with second and third degree burns overthe face and upper extremities, including both hands, as a result of ahouse fire. A large mitten-shaped reduced pressure appliance of thegeneral type shown in FIGS. 1 and 10 is placed over the patient's righthand, with open cell foam inserts placed between the fingers to applyreduced pressure to the interdigit spaces. Three pounds of vacuum isapplied cyclically in a pattern of five minutes on, 5 minutes off. Theappliance is changed on a three times per week schedule. Treatment iscontinued until the necrotic tissue sloughs off or is excised, followedby split thickness skin graft placement.

EXAMPLE 4

[0072] Treatment of Flaps

[0073] In order to determine the effect of reduced pressure applicationupon skin flap survival, five 15 kg Chester pigs were obtained andacclimated for 1 week as described previously. Two dorsally-based 3 cmby 12 cm flap outlines were drawn using indelible ink on each side ofthe pigs, leaving 6 cm between each flap. The flaps were assigned to oneof four groups as follows:

[0074] (1) Dual-treated flaps are flaps that were exposed to reducedpressure both prior to and following surgery;

[0075] (2) Pre-treated flaps are flaps that were exposed to reducedpressure prior to surgery, but were not exposed to reduced pressureafter surgery;

[0076] (3) Post-treated flaps are flaps that were exposed to reducedpressure following surgery; and

[0077] (4) Control flaps are flaps that were not exposed to reducedpressure either pre- or post-surgery.

[0078] The pre-treated flaps were initially treated by covering an areasurrounding one of the flap outlines on the left side of each animalwith a reduced pressure appliance of the type shown in FIGS. 1 and 10having a large piece of open cell foam into which a tube was inserted.The foam was covered and sealed to the flap area with impermeableadherent sheeting. A reduced pressure of 7 pounds was then continuouslyapplied to the area for 7 days.

[0079] On the day of surgery, each pig was sedated as previouslydescribed and anesthesia was maintained by 1% halothane. Two 3 cm by 12cm dorsally based flaps were created on each side of the pig followingthe flap outlines. The flaps were created at a depth immediately belowthe panniculus carnosus (a subcutaneous muscle layer). The flaps wereraised and then sutured back in place with single, interrupted suturesof 3-0 nylon. The reduced pressure appliances were then placed over theanterior flaps on each side of the animal. A reduced pressure of 5-7pounds was continuously applied to the anterior flaps. Each suction tuberan from the appliances on the animals upward through a pulley suspendedover the pens and down to a vacuum trap bottle to collect any liquidexudate. A hose was connected from each vacuum trap bottle to a vacuumpump to supply the reduced pressure to the appliances. The animals hadfree access to all areas of the pen.

[0080] The animals were anesthetized 72 hours after surgery and theappliances were removed. Photographs of each side of the animals weretaken, and tracings of the flaps (and encompassing any discolored areas)were made on acetate to allow for planimetric calculation of percentsurvival. The appliances were then replaced and reduced pressurere-applied. This routine was continued at 48 hour intervals until nofurther necrosis or healing of the flaps was observed.

[0081] The distal portions of all flaps were discolored 72 hours postsurgery, with the flaps exposed to reduced pressure being lighter incolor. The distal ends of all flaps appeared to necrose and an escharformed over the distal portion of each flap. Over time the escharspontaneously desquamated, exposing the outline of the original flap.The eschar over the control and pre-treated flaps consistentlydesquamated sooner than the post-treated and the dual-treated flaps. Thecontrol flaps had contracted to a Y shape which was evident after theeschar had desquamated. The dual-treated flaps had contracted slightlyand appeared as long, thin rectangles after dislodgement of the eschar.The pre-treated flaps and post-treated flaps were intermediate betweenthe control and dual-treated flaps in regard to flap contraction.

[0082] Dual-treated flaps exhibited the greatest survival in terms ofpercent retention (72.2%) of the original flap size. The post-treatedflaps had the second greatest survival (67.4%). The pretreated flaps hadthe third most flap survival (64.8%). The control flaps had the leastflap survival (51.2%). All treated flaps (dual-treated; pre-treated; andpost-treated) exhibited significantly greater surface area survival thanthe control flaps. The dual-treated flaps had significantly greatersurface area survival than either the pre-treated or post-treated flaps.The pre-treated flaps were not significantly different than post-treatedflaps in regard to flap survival.

EXAMPLE 5

[0083] Treatment of Decubitus Ulcers

[0084] Application of reduced pressure was tested upon chronic decubitusulcers and was found to be effective in the treatment thereof. Necroticsoft tissue was removed from the ulcers prior to placement upon thetreatment site of a reduced pressure appliance of the type described inconnection with FIGS. 1 and 10. Treatment of decubitus ulcers was testedusing both continuous and cyclic application of reduced pressure. It wasfound that cyclic application of reduced pressure was both moreeffective and produced less discomfort for the patients than continuousapplication. Cyclic application of reduced pressure was conductedaccording to an application schedule of 5 minutes of suction followed by5 minutes of non-suction. In 15 patients tested, successful treatmentrequired from 2 to 13 weeks. Thirteen of the ulcers healed completelyand every ulcer treated demonstrated progressive decrease in size duringtreatment. The following case histories demonstrate the manner in whichvarious pressure sores were treated:

[0085] Case 1

[0086] A 39 year-old male T4 paraplegic had suffered from multiplerecurrent pressure sores over a period of 8 years. He had been treatedfor a trochanteric decubitus with a tensor fascia lata flap which haddeveloped a recurrent ulcer in the center of the flap 4 months prior topresentation. The ulcer was debrided of necrotic tissue to non-involvedperiosteum resulting in a wound measuring 12 cm by 5 cm with a depth of5 cm. During the course of 4 weeks of cyclic reduced pressureapplication, the wound progressively closed and spontaneouslyre-epithelialized. Reduced pressure of 5 in. Hg below atmosphericpressure was applied cyclically with 5 minute intervals of appliedpressure followed by 5 minute intervals with no applied pressure. Thewound remained healed more than 5 months after treatment.

[0087] Case 2

[0088] A 45 year old male paraplegic suffered from a recurrent rightischial fossa pressure sore and abscess prior to treatment. Debridementof the wound was carried out with partial ischial resection. A weeklater, a re-advancement of the V-Y biceps femoris flap and rotationgluteus flap was performed. Six days later, the wound dehisced and thepatient developed bilateral pneumonia requiring ventilatory support. Theflap became progressively edematous and firm and resisted all efforts atmobilization. At this point, reduced pressure treatment providingcontinuous, non-cyclic suction or a vacuum at approximately five 5 in.Hg below atmospheric pressure was initiated. A total of 2 liters offluid was removed by the reduced pressure appliance during the first 72hours of treatment. Intravenous fluids were administered to replace thefluid removed from the wound. The appliance was replaced and the woundwas examined three times each week. Treatment was continued for a totalof six weeks during which the flap became progressively less indurated,granulation tissue formation rapidly progressed, the edges of the woundcame into approximation, and the wound was healed completely.

[0089] Case 3

[0090] A 51 year-old T1 paraplegic had multiple previous pressure soresculminating in bilateral asynchronous hip disarticulations and bilateraltotal thigh flaps. Seven months prior to admission, he developed a 7 cmby 23 cm pressure sore over the remnants of both ischia. Bone wasexposed and no tissue was available for wound closure. Dressing changesover a period of three months had failed to improve the wound. A reducedpressure appliance was then secured to the wound. During the first 3weeks of treatment, reduced pressure of 5 in. Hg below atmosphericpressure was continuously applied. For the following 9 weeks, reducedpressure was applied cyclically in 5 minute intervals. The appliance wasreplaced every three days during treatment. In the course of thetreatment, the wound first granulated to cover the bone completely andthen the wound re-epithelialized from the margins. After 12 weeks of thetreatment, a 2 cm by 5 cm scrotal flap was used to cover the midlinearea of the wound. The wound has remained stable beyond 6 months aftertreatment.

EXAMPLE 6

[0091] Treatment of Dehisced Incisions

[0092] A 50 year old debilitated white male who had undergone acolostomy through a midline laparotomy was re-admitted to the hospitalfor wound dehiscence and evisceration following an upper respiratoryinfection. He was taken immediately to the operating room and theabdominal wall was closed with Prolene mesh. Six weeks after placementof the Prolene mesh, the wound was still open and measured 28 cm by 23cm. Only sparse granulation tissue had grown through the Prolene meshduring the six weeks. At this time a large reduced pressure appliance ofthe type shown in FIG. 5 was placed on an underlying porous aquaplastsheet (WFR/Aquaplast Corp., Wycoff, N.J. 07481) over top of the Prolenemesh/wound surface and the space closed with a covering tent of Ioban. Acontinuous vacuum of 5 in. Hg below atmospheric pressure was applied.The appliance was changed three times per week. After 8 days oftreatment, granulation tissue had grown through and totally covered theProlene mesh. Two days later, the patient was taken to the operatingroom, where the surrounding tissue was undermined and used to close 75%of the wound. Split thickness skin grafts were used to cover theremainder of the wound, and were placed on the bed of granulationtissue. There was 80% take of the grafts, and the remaining areas healedspontaneously with wet to dry dressing changes. The wound has remainedstable 16 months after surgery.

EXAMPLE 7

[0093] Treatment of Infected Wound

[0094] Infected wounds have been successfully treated via application ofreduced pressure as described in the following cases:

[0095] Case 1

[0096] A 39 year old white male sustained severe avulsive trauma to hisleft lower extremity in a motor vehicle accident 10 years prior topresentation. He presented with a ten year history of chronicosteomyelitis and a 3 cm diameter open ulcer with exposure of bone ofhis left lateral malleolus. He had previously undergone 7 local surgicalprocedures to attempt closure of the wound. An arteriogram demonstrateda one vessel foot with diffuse atherosclerosis and post traumaticchanges. The extremity was debrided of necrotic soft tissue and allinvolved bone saucerized. The patient was placed on a five week courseof antibiotics. The day after debridement, a reduced pressure device ofthe type shown in FIGS. 2 and 11 was applied over the wound and areduced pressure of 5 in. Hg below atmospheric pressure was applied. Thedevice was changed on a three times per week schedule. After 14 days oftreatment, the wound was smaller and filled with granulation tissuewhich completely covered the previously exposed bone. A split thicknessskin graft was placed over the wound and healed primarily. The wound hasbeen stable for 13 months with no recurrence of osteomyelitis or tissuebreakdown.

[0097] Case 2

[0098] A 51 year old white male T8 paraplegic was admitted to thehospital for an infected left trochanteric pressure sore which had beenpresent for one year and measured 4 cm by 6 cm. The patient hadpreviously undergone multiple procedures for treatment of this conditionincluding a V-Y advancement flap 4 months prior to presentation. A scanrevealed possible chronic osteomyelitis of the left femur. It wasdecided to treat the potential osteomyelitis with a five week course ofIV antibiotics. The wound was debrided, then treated using a reducedpressure appliance of the type shown in FIGS. 1 and 10 for 6 weeks withcyclical reduced pressure (5 in. Hg below atmospheric pressure; 5minutes on/5 minutes off). The wound rapidly granulated and decreased insize. After 6 weeks the wound had closed and the patient discharged. Thepatient was readmitted 1 month later with a draining sinus tract to thebone. The previously scanned head of the left femur was resected and thewound closed primarily over drains. The wound healed without furtherproblems.

EXAMPLE 8

[0099] Chronic open Wound Secondary to Stasis Ulcers

[0100] A 45 year old black female patient with a 10 year history ofbilateral stasis ulcers of the pretibial area was presented withbilateral 10 cm by 15 cm infected ulcers with exposed fascia. Twoprevious attempts at skin grafting in the previous year had failed. Thepatient was treated using a reduced pressure appliance of the type shownin FIGS. 1 and 10 for 14 days with cyclical (5 minutes on/5 minutes off)reduced pressure of approximately 5 in. Hg below atmospheric pressure.After 14 days treatment, quantitative bacterial counts of both ulcerswere below 102 bacteria/gram tissue, and both ulcers appeared as healthygranulating beds. Split thickness skin grafts were then applied andexhibited 100% take. The patient is ambulating, and the wounds haveremained healed for 2 months, which is the longest the wounds had beenhealed in the last 10 years.

EXAMPLE 9

[0101] Enhancement of Blood Flow

[0102] It is believed that the efficacy of reduced pressure appliancesin such treatments as have been described is due at least in part toenhancement of blood circulation within the treated wounds. In order todetermine the effect of pressure application upon blood flow, a laserdoppler needle probe was inserted is into tissue adjacent to a pressuresore. A baseline flow level was recorded for thirty minutes. Then, therelative blood flow level was measured while a reduced pressurecorresponding to 5 in. Hg below atmospheric pressure was continuouslyapplied to the wound for 30 minutes using a reduced pressure applianceof the type shown in FIGS. 1 and 10. During continuous reduced pressureapplication, the relative blood flow level was only slightly higher thanthe baseline level.

[0103] Then the supply of reduced pressure to the appliance was cycledon and off at equal 5 minute intervals. During the “off” portions of thecycle, the relative blood flow level was twice as high as the baselinelevel. It is postulated that the increased blood flow during the offcycle is likely due to a “rebound” phenomenon. During the “on” cycle,blood is drawn toward the wounded tissue from both the venous andarterial branches of the vascular network in the vicinity of the wound.During the “off” cycle, this blood is transported toward the venousbranch-of the vascular network at a rate that is greater than would havebeen observed in the absence of the preceding “on” cycle.

[0104] The terms and expressions which have been employed are used asterms of description and not of limitation and there is no intention inthe use of such terms and expressions of excluding any equivalents ofthe features shown and described, or portions thereof, but it isrecognized that various modifications are possible within the scope ofthe claimed invention.

1. An apparatus for facilitating the healing of wounds, comprising:sealing means for maintaining a reduced pressure on a wound bycontacting the skin surrounding the wound; reduced pressure supply meansoperably connected with the sealing means for connection to a vacuumsource, the reduced pressure supply means cooperating with said sealingmeans to supply and maintain the reduced pressure beneath the sealingmeans; and screen means for positioning within the depth of the woundand within the sealing means.
 2. The apparatus according to claim 1 ,wherein the reduced pressure supply means comprises a generally tubularmember.
 3. The apparatus according to claim 2 , wherein the generallytubular member is operatively connected to the screen means.
 4. Theapparatus according to claim 3 , wherein the generally tubular membercomprises a side port for promoting a substantially uniform applicationof reduced pressure within the sealing means.
 5. The apparatus accordingto claim 3 , wherein the generally tubular member includes a first openend embedded within the screen means.
 6. The apparatus according toclaim 5 , wherein the screen means is adapted to substantially preventthe sealing means from forming sealing contact with the first open endof the tubular member.
 7. The apparatus according to claim 1 , whereinthe screen means comprises foam.
 8. An appliance for administering areduced pressure treatment to a wound comprising: (a) a cover adapted tocover and enclose the wound and to maintain reduced pressure at the siteof the wound; (b) an adhesive layer disposed at the periphery of thecover for sealing said cover to tissue surrounding the wound; and (c) areduced pressure supply means operably connected with the cover forconnection to a source of suction, said reduced pressure supply meanscooperating with said cover to supply and maintain said reduced pressurebeneath the cover.